Switching activation of ue receviers

ABSTRACT

In some implementations, a method for managing a receiver for user equipment in a Long Term Evolution (LTE) system includes activating the UE receiver during a control portion of a sub-frame including control information. After receiving the control portion, the UE receiver is deactivated during a data-traffic portion of the sub-frame.

CLAIM OF PRIORITY

This application claims priority under 35 U.S.C. §119(e) to U.S.Provisional Patent Application Ser. No. 61/481,105, filed on Apr. 29,2011, the entire contents of which are hereby incorporated by reference.

BACKGROUND

This document relates to wireless communications in wirelesscommunication systems.

As used herein, the terms “user equipment” and “UE” can refer towireless devices such as mobile telephones, personal digital assistants(PDAs), handheld or laptop computers, and similar devices or other UserAgents (“UA”) that have telecommunications capabilities. In someembodiments, a UE may refer to a mobile, wireless device. The term “UE”may also refer to devices that have similar capabilities but that arenot generally transportable, such as desktop computers, set-top boxes,or network nodes.

In traditional wireless telecommunications systems, transmissionequipment in a base station or other network node transmits signalsthroughout a geographical region known as a cell. As technology hasevolved, more advanced equipment has been introduced that can provideservices that were not possible previously. This advanced equipmentmight include, for example, an evolved universal terrestrial radioaccess network (E-UTRAN) node B (eNB) rather than a base station orother systems and devices that are more highly evolved than theequivalent equipment in a traditional wireless telecommunicationssystem. Such advanced or next generation equipment may be referred toherein as long-term evolution (LTE) equipment, and a packet-basednetwork that uses such equipment can be referred to as an evolved packetsystem (EPS). Additional improvements to LTE systems and equipmentresult in an LTE advanced (LTE-A) system. As used herein, the phrase“base station” will refer to any component or network node, such as atraditional base station or an LTE or LTE-A base station (includingeNBs), that can provide a UE with access to other components in atelecommunications system.

In mobile communication systems such as E-UTRAN, a base station providesradio access to one or more UEs. The base station comprises a packetscheduler for dynamically scheduling downlink traffic data packettransmissions and allocating uplink traffic data packet transmissionresources among all the UEs communicating with the base station. Thefunctions of the scheduler include, among others, dividing the availableair interface capacity between UEs, deciding the transport channel to beused for each UE's packet data transmissions, and monitoring packetallocation and system load. To facilitate communications, a plurality ofdifferent communication channels may be established between a basestation and a UE. The scheduler dynamically allocates resources forPhysical Downlink Shared CHannel (PDSCH) and Physical Uplink SharedCHannel (PUSCH) data transmissions, and sends scheduling information tothe UEs through a Physical Downlink Control CHannel (PDCCH).

As the label implies, the PDCCH is a downlink channel that allows thebase station to control a UE during data communications. To this end,the PDCCH is used to transmit control information within control datapackets referred to as Downlink Control Information (DCI) messages. Thecontrol information conveyed within DCI messages may be used to transmituplink or downlink scheduling assignments (for PUSCH and PDSCHrespectively) or to convey other control information. The controlinformation may be directed towards or addressed to one UE, a group ofUEs, or all UEs within the cell. Downlink scheduling assignments may besent to a UE to indicate to the UE parameters related to the formattingof a forthcoming transmission of downlink communication traffic packetsby the base station on a Physical Downlink Shared Channel (PDSCH) and toindicate the location of the physical resources to be used for thattransmission. Uplink scheduling assignments may be sent to a UE toindicate parameters related to a forthcoming transmission of uplinkcommunication traffic packets by the UE on a Physical Uplink SharedChannel (PUSCH) and to indicate the location of the physical resourceson which the transmission may take place. DCI messages may also conveyother types of control information or provide specific instructions tothe UE (e.g., power control commands, an order to perform a randomaccess procedure, or a semi-persistent scheduling activation ordeactivation). A separate DCI packet may be transmitted by the basestation to a UE for each traffic packet/sub-frame transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates an example a wireless system architecture;

FIG. 1B illustrates an example Long Term Evolution (LTE) system;

FIG. 1C illustrates RRC connection states and DRX sub-states in LTE;

FIG. 1D illustrates an example downlink sub-frame;

FIG. 1E is a diagram illustrating assignment message construction andmapping to PDCCH;

FIGS. 2A and 2B are flow charts for illustrating methods for explicitlytransitioning the states of the UEs;

FIGS. 3A and 3B are flow charts for illustrating methods for implicitlytransitioning the states of the UEs;

FIG. 4 illustrates an example sub-frame;

FIG. 5 illustrates a schematic diagram illustrating a process formanaging a receiver of a user equipment;

FIG. 6A-C are schematic diagrams illustrating sequences when no data istransmitted;

FIG. 7 is a codeword system illustrating a set of wake-up indicatorsbeing encoded and decoded;

FIGS. 8A-D are mappings between codewords and values of wake-upindicators;

FIG. 9 is a schematic diagram illustrating time domain multiplexing ofwake-up messages within a DRX cycle length;

FIG. 10 is a schematic diagram that illustrates a single-user wake-upmessage addressed to a UE-specific RNTI;

FIGS. 11A and 11B are schematic diagrams illustrating wake-up usingnormal DL assignment on PDCCH but with delayed PDSCH; and

FIG. 12 shows an example of a radio station architecture

DETAILED DESCRIPTION

FIG. 1A shows an example of a wireless communication system. A wirelesscommunication system includes one or more radio access networks 135 andone or more core networks 125. Radio access networks 135 a and 135 binclude one or more base stations (BSs) 105 a, 105 b. The system mayprovide wireless services to one or more wireless devices 110 a, 110 b,110 c, and 110 d. Base stations 105 a and 105 b can provide wirelessservice to wireless devices 110 a-d in one or more wireless sectors. Insome implementations, base stations 105 a, 105 b use directionalantennas to produce two or more directional beams to provide wirelesscoverage in different sectors. A core network 125 communicates with oneor more base stations 105 a and 105 b. In some implementations, a corenetwork 125 includes one or more base stations 105 a and 105 b. The corenetwork 125 may include wireless communication equipment such as one ormore servers. In some implementations, the core network 125 is incommunication with a network 130 that provides connectivity with otherwireless communication systems and wired communication systems. Thewireless communication system may communicate with wireless devices 110a-d using a wireless technology such as one based on orthogonalfrequency division multiplexing (OFDM), Orthogonal Frequency DivisionMultiple Access (OFDMA), Single Carrier Frequency Division MultipleAccess (SC-FDMA), Discrete Fourier Transform Spread Orthogonal FrequencyDivision Multiplexing (DFT-SOFDM), Space-Division Multiplexing (SDM),Frequency-Division Multiplexing (FDM), Time-Division Multiplexing (TDM),Code Division Multiplexing (CDM), or others. The wireless communicationsystem may transmit information using Medium Access Control (MAC) andPhysical (PHY) layers. The techniques and systems described herein maybe implemented in various wireless communication systems such as asystem based on Long Term Evolution (LTE) Global System for MobileCommunication (GSM) protocols, Code Division Multiple Access (CDMA)protocols, Universal Mobile Telecommunications System (UMTS), UnlicensedMobile Access (UMA), or others.

Wireless devices, such as smartphones, may generate and consumesignificant amounts of data over a wide variety of data traffic typesand services. Smartphone devices may be viewed as computing platformswith wireless connectivity, capable of running a wide-ranging variety ofapplications and services that are either pre-installed by the devicemanufacturer or installed by the user according to the user's specificusage requirements. The applications may originate from a wide-ranginggroup of sources such as software houses, manufacturers, and third-partydevelopers.

Wireless networks may distinguish between user-plane traffic andcontrol-plane traffic. Various examples of user-plane traffic andservices carried by wireless networks include voice, video, internetdata, web browsing sessions, upload/download file transfer, instantmessaging, e-mail, navigation services, RSS feeds, and streaming media.Control-plane traffic signaling may be used to enable or supporttransfer of the user plane data via the wireless network, including, forexample, mobility control and radio resource control functionality.Various examples of control plane traffic include core-network mobilityand attachment control, (e.g., Non-Access Stratum (NAS) signaling),radio access network control (e.g., Radio Resource Control (RRC)), andphysical layer control signaling such as may be used to facilitateadvanced transmission techniques and for radio link adaptation purposes.

Applications, communicating via a wireless network, may utilizeInternet-based protocols to achieve a desired effect when provisioningfor a specific service. For example, a navigation application mayutilize TCP for file transfer of mapping data from a server to a device.The navigation application may use periodic keep-alive signaling (e.g.,exchanging PING messages) towards the navigation server to maintain anapplication-level connection in the presence of intermediary networknodes such as stateful firewalls. Similarly, an e-mail application mayuse a synchronization protocol to align mailbox contents on a wirelessdevice with those in the e-mail server. The e-mail application may use aperiodic server polling mechanism to check for new e-mail.

Wireless network designs are influenced by the data demands produced byvarious applications and associated data traffic distributions. Forexample, the amount and timing of data traffic may vary (e.g., burstycommunications). To adapt, wireless communication networks may includedynamic scheduling such that a quantity of assigned shared radioresources may be varied in rapid response to data demand (e.g., databuffer status). Such dynamic scheduling can operate on a time scale ofone to two or three milliseconds. At a time scale above this (e.g.,operating in the region of 100 milliseconds to several seconds),wireless networks can use a state-machine-oriented process or othersystem reconfiguration process to adapt a radio connection state orsub-state to the degree of observed traffic activity. Radio connectionstates or sub-states may differ both in the degree of connectivityoffered and in terms of the amount of battery power consumed by awireless device.

A connectivity level can be characterized as representing connectivityattributes, such as location granularity, assigned resources,preparedness, and interfaces or bearers established. A locationgranularity attribute may be the accuracy to which a wireless networkcan track the current location of a wireless device (e.g., to the celllevel for more active devices, or to only a group of cells for lessactive devices). Examples of assigned resource attributes include thepresence, absence, type or amount of radio transmission resourcesavailable to the wireless device for performing communication, as afunction of expected activity level.

A preparedness attribute is an ability of a wireless device to receiveor transmit information. The power consumed by wireless devices mayreflect a function of an ability of a wireless device (or readiness) totransmit or receive. For example, a wireless device can activate itsreceiver in order to receive downlink communication from a base stationat any given instant, which may cause higher power consumption andbattery drain. To save power, a mode referred to as discontinuousreception (DRX) may be used. In DRX, the wireless device can place itsreceiver in a sleep mode, e.g., turning off its receiver at certaintimes. The base station uses knowledge of a UE's DRX pattern (e.g.,sequence of wake-up intervals of the device) when determining times totransmit to a wireless device that is in a DRX mode. For example, a basestation determines a time in which the wireless device will be activelylistening for a transmission. The activity cycle of a DRX pattern canvary as a function of an assigned radio connection state or sub-state.

Interfaces (or bearers-established) attributes are other examples ofconnectivity attributes. End-to-end communications (e.g., from awireless device to a core network gateway or egress node towards theInternet) can require that user-specific connections, or bearers, areestablished between participating network nodes or entities. User-planeconnectivity through a radio access network and a core network canrequire the establishment of one or more network interfaces betweenvarious pairs of network nodes. The establishment of one or more ofthese network interfaces can be associated with a radio connection stateor sub-state as a function of the current activity level.

FIG. 1B is an LTE system 140 for managing activation of a receiver ofthe UEs 145 a and 145 b in accordance with some implementations of thepresent disclosure. For example, the system 140 may be arranged to allowdeactivation of a UE receiver during one or more portions of time knownas discontinuous reception instances (DRX). During other portions oftime (non-DRX), the UE receiver may be activated. The portions of timemay comprise one or more time units known as sub-frames, a sub-framehaving a duration of 1 millisecond. A periodic cycle known as a DRXcycle may be configured and which defines those sub-frames that aredesignated as non-DRX. During a non-DRX sub-frame within a DRX cycle,the UE may receive a PDCCH region of the sub-frame and must also beprepared to receive a Physical Downlink Shared CHannel (PDSCH). In someimplementations, the system 140 includes a “wake-up” signal within thePDCCH region of the sub-frame for LTE connected mode UEs, and thewake-up signal may have carefully designed properties such that systemefficiency and UE battery efficiency are improved. The system 140 may ormay not add new Radio Resource Control (RRC) states to execute the UEreceiver management. For example, the system 140 may retain the idlemode and connected mode RRC states only, or a new RRC state may beintroduced. In the case that no new RRC states are introduced, aconnected mode UE (for example one that may have been inactive forlonger than a predetermined period of time), may be placed into a“connected mode deep sleep” (or CMDS) sub-state of connected mode. Byadding the CMDS sub-state, the system 140 may provide additional systemefficiency and UE battery savings. For example, the UE may not searchfor UE-specific uplink and downlink assignments during non-DRXsub-frames when in the CMDS sub-state (it does not need to be ready toreceive immediate user plane data on those sub-frames). A UE in the CMDSsub-state may instead search only for a connected-mode wake-up signalduring a non-DRX sub-frame. This allows for processing complexityreductions in the UE during any non-DRX'd sub-frame. In another example,the UE may be addressable via group wake-up Radio Network TemporaryIdentifier (RNTIs) when in the CMDS sub-state (as compared withdedicated UE-specific RNTIs), such that the system may efficientlywake-up multiple devices within the same PDCCH message and during thesame sub-frame. In some implementations, the UE may only receive thePDCCH region for the wake-up signal (the network may not be allowed tosend PDSCH to the UE during the same sub-frame as a wake-up). This mayallow the UE to switch off its RF, analogue and front-end receivercircuitry (e.g., element 1215 of FIG. 12) immediately following thePDCCH region of any non-DRX sub-frame, irrespective of the PDCCHprocessing/decoding latency. This may allow for a substantially lowerfraction of time for which the receiver must be on when operating undera DRX cycle. For example, it may allow for the receiver to be on foronly 3 OFDM symbols of each actively-received sub-frame rather than for14 symbols (a reduction of 78% in receiver “on” time for the samesub-frame DRX duty cycle). Conversely, it may allow for shorter DRXcycles (providing lower latency) but without a corresponding increase inUE power consumption.

In the illustrated implementation, the LTE system 140 can include a corenetwork called an Evolved Packet Core (EPC) and an LTE Radio AccessNetwork, e.g., evolved UTRAN (E-UTRAN). The core network providesconnectivity to an external network such as the Internet 170. The systemincludes one or more base stations such as eNode-B (eNB) base stations150 a and 150 b that provide wireless service(s) to one or more devicessuch as UEs 145 a and 145 b.

An EPC-based core network can include a Serving Gateway (SGW) 160, aMobility Management Endpoint (MME) 155, and a Packet Gateway (PGW) 165.The SGW 160 can route traffic within a core network. The MME 155 isresponsible for core-network mobility control, attachment of the UE 145to the core network and for maintaining contact with idle mode UEs. ThePGW 165 is responsible for enabling the ingress/egress of trafficfrom/to the Internet 170. The PGW 165 can allocate IP addresses to theUEs 145.

An LTE-based wireless communication system has network interfacesdefined between system elements. The network interfaces include the Uuinterface defined between a UE and an eNB, the S1U user-plane interfacedefined between an eNB and an SGW, the S1C control-plane interfacedefined between an eNB and an MME (also known as S1-MME), and the S5/S8interface defined between an SGW and a PGW. Note that the combination ofS1U and S1C is often simplified to “S1.”

A wireless device can transition between connection states, such as RRCconnection modes. In the LTE system, two RRC connection modes exist, RRCconnected and RRC idle. In an RRC connected mode, radio and radio accessbearers (e.g., the Uu and S1 bearers) are established to enable thetransfer of user plane data through a radio access network and onwardsto the core network. In the RRC idle mode, radio and radio accessbearers are not established and user-plane data is not transferred. Insome implementations, a limited degree of control signaling is possiblein idle mode to enable the wireless network to track the location of thedevice should a need for communications arise.

A wireless device, in an RRC-connected state, can use a DRX operationalmode to conserve power by turning-off transceiver functionality, e.g.,turning-off transceiver circuitry such as receiver circuitry. In someimplementations, a wireless device ceases to monitor a wireless channeland, accordingly, ceases to operate a digital signal processor to decodewireless signals while in the DRX operational mode.

FIG. 1C shows an example of a transition diagram for RRC and DRX. RRCconnection states include an RRC connected state 180 and an idle state182. Transitions between the idle state 182 and the connected state 180are effected via RRC establishment and release procedures. Suchtransitions can produce associated signaling traffic between a wirelessdevice and a base station.

UE DRX functionality may comprise a mechanism to control when the UEmonitors a wireless grant channel such as the downlink Physical CommonControl Channel (PDCCH) in LTE by application of discontinuousreception. The specific times during which the UE may be active andcapable of reception may be described by a time-domain pattern known asa DRX cycle. The time domain pattern may vary or may be reconfigured asa function of a data activity level. Such a variation or reconfigurationmay further be triggered or controlled by timers. For a particularcommunication between a network and a UE, a plurality of possible DRXcycle configurations may exist and one of the plurality may be selectedin accordance with a desired system operation for the communication. Insuch a case, the system may include a plurality of DRX sub-states and acontroller configured to select an appropriate DRX sub-state from theplurality of DRX sub-states based, at least in part, on a desired systemoperation. Parameters or timers controlling or defining the DRX cyclemay be associated with each of the plurality of DRX sub-states accordingto system configuration. In some implementations, DRX sub-states per-semay not be explicitly implemented and in such a case the term “DRXsub-state” may refer only to a particular configuration of parameters orcondition of one or more timers (e.g., running or not running). The term“DRX sub-state” may therefore be used interchangeably with “DRX status”of DRX-related parameters or timers; hence, a configured plurality ofDRX-related parameters may be referred to as a DRX sub-state.

The RRC connected mode state 180 may be associated with a plurality ofDRX sub-states (or DRX status) within the Medium Access Control (MAC)layer. The DRX sub-states (or DRX status) include a continuous reception(continuous-rx) state 184, a short DRX state 186, and a long DRX state188. In the continuous reception state 184, a device may be continuouslymonitoring all or almost all downlink sub-frames for wireless trafficand can transmit data. In the short DRX state 186, the device can becontrolled to turn off its receiver (e.g., sleep, or DRX) for all but Qout of N sub-frames. In the long DRX state 188, the device can becontrolled to turn off its receiver (e.g., sleep, or DRX) for all but Qout of M sub-frames, where M is typically greater than N. In oneexample, Q equals 1, N equals 8 and M equals 256. In an LTE-basedsystem, a sub-frame is a 1 millisecond unit of transmission time.

In some implementations, an expiration of an inactivity timer causes astate transition (e.g., continuous reception state 184 to short DRXstate 186 or short DRX state 186 to long DRX state 188). Resumption ofactivity, such as the device having data to transmit or receiving newdata, can cause a transition from a DRX state 186, 188 to the continuousreception state 184. In some implementations, a base station sends a MACcommand that causes a transition from the continuous reception state 184to one of the DRX states 186, 188. In other words, MAC commands may alsobe used by the network (sent from eNB to the UE) in order to explicitlydirect a transition to a different DRX sub-state with a longer DRXcycle. A resumption of data activity typically results in a transitionto the continuous reception sub-state. Transitions between Idle andConnected Mode may be effected using explicit RRC establishment andrelease signaling procedures, which involves associated signalingoverheads. The base station's decision to send a MAC command to causethe UE to transition to another DRX sub-state may be based on timerswithin the network, or may be based on a plurality of other factors orevents. In one improved method, the base station may send the MACcommand in response to a fast dormancy request received from the UE, thefast dormancy request indicating the UE's desire to be transitioned to amore battery-efficient state, the more battery-efficient statecomprising a new DRX sub-state or new DRX status. The UE may transmit afast dormancy request (e.g., explicit message, indication message) tothe network based on a determination that no more data transfer islikely for a prolonged period. For example, the UE may transmit theexplicit message (e.g., an indication message) requesting an updatedsub-state to a more battery efficient sub-state and the request torelease resources. In some implementations, the explicit message (orindication message) may be a Signaling Connection Release Indication(SCRI) message. The UE's step of determining may involve an appraisal ofcurrently-operational applications or processes running on the mobiledevice, and/or the status of acknowledged mode protocols or acknowledgedmode transfer of data. For example, if the UE is aware that a particulardata transfer has ended due to its reception of an acknowledgementmessage, the UE may decide to send a fast dormancy request to thenetwork. The network may respond with a message to the UE to indicatethat it should move to a new DRX sub-state or to otherwise alter its DRXstatus. This message may be sent within a MAC CE command or may be sentwithin a physical layer message such as on a PDCCH. In the improvedmethod, receipt of the message at the UE not only triggers a transitionto a new DRX sub-state or a change in DRX status, but also triggers arelease of assigned uplink control resources. Thus, by use of thisimproved method, the network does not need to send a further messagespecifically for the purposes of releasing the uplink resources, andsignaling overheads are thereby reduced.

In each of these DRX sub-states, both the UE and network can, in someimplementations, be synchronized in terms of the currently-applicableDRX status or DRX sub-state such that both the network and UE identifywhen the UE receiver is active and when the UE receiver may be “off”,“asleep” or otherwise inactive. Within the connected mode, thesynchronization may be achieved using network-configured timers and/orparameters.

The LTE system may also provide for DRX battery saving in RRC Idle. Whenin Idle Mode, the UE may employ a DRX pattern according to a so-calledpaging cycle. On a possible paging occasion, the UE may activate itsreceiver to check for a page message sent by the network. At othertimes, the UE may deactivate its receiver in order to conserve power.

Based on the illustrated transition diagram, within the LTE system, twodifferent approaches may be employed to control the UE's RRC state as afunction of data activity or inactivity. In the first approach, inactivedevices may be transitioned to idle mode relatively quickly. Aresumption of data activity may invoke execution of RRC connectionestablishment procedures and may incur signaling overhead. In the secondapproach, inactive devices may be held for a considerable time (forexample, many minutes, even hours) in RRC Connected Mode before atransition to idle is executed.

A UE may have a lower power consumption in RRC idle mode than in RRCConnected Mode; therefore, from a UE power consumption perspective, thefirst approach may provide power saving advantages when compared to thesecond approach. However, to transfer those UEs that have been inactivefor a period of time to the RRC idle state may require use of anexplicit RRC connection release message sent by the eNB to the UE. AnRRC connection setup procedure may also be used upon each resumption ofdata activity. Hence, whilst the first approach can be batteryefficient, the first approach may include potentially large signalingoverheads and therefore lower system efficiency.

The signaling overheads associated with the first approach may besubstantially avoided using the second approach. Though, the secondapproach may include increased battery consumption by the mobile device(this being a function of how battery efficient the DRX procedures arewhen in connected mode). Furthermore, power consumption within an RRCconnected mode DRX sub-state may also be higher than that of Idle Modedue to the use of network controlled mobility when in RRC ConnectedMode. In Connected Mode, the UE typically sends signal strength/qualitymeasurement reports to the eNB either periodically, or on a triggeredbasis (for example, on detection of deteriorating signal conditions).The eNB may then be in control of when to direct the UE to hand over toanother cell. Conversely, in RRC Idle Mode, mobility may beUE-controlled. That is, the UE may not report the signalstrength/quality of other cells to the network but may use its ownmeasurements of such to select the preferred cell. Cells within thenetwork may be arranged into logical groups known as tracking areas,each of which may consist of a plurality of cells. When in RRC IdleMode, the UE may notify the network when changing to a cell within a newtracking area. This process (known as a tracking area update) typicallyoccurs relatively infrequently and, in addition to the infrequentpaging/DRX cycles, may reduce UE battery consumption whilst in the RRCIdle Mode.

The first approach may be referred to as a “call-oriented” model. Aburst of data activity may be treated similar to a phone call or othercommunication session, wherein at a macro level the packet data “call”is either “on” or “off”. Within a packet data call and on a micro timescale, data activity may not be continuous, but the packet call may betreated as “active” or “in-call” by the network for a relatively shortperiod of time. The UE may be held in the RRC connected mode for theduration of the packet call. For sustained inactivity beyond thisrelatively short period of time, the UE may transition to Idle. Withthis understanding, a packet call can, in some implementations, comprisea burst of packet activity spanning only a few hundred milliseconds orup to a few seconds, for example, when downloading a particular web pagefrom the internet. Subsequent packet calls with associated transitionsto/from Idle may exist for other web pages accessed perhaps 20 secondslater.

FIG. 1D is a downlink sub-frame 185 illustrating the time/frequencystructure. The sub-frame 185 is sub-divided into two equal length slots(numbered here n and n+1). In the time domain, the PDCCH region 186comprises the first 3 out of the 14 total OFDM symbols (OS) within thesub-frame. An assignment to a UE may be contained somewhere within thePDCCH region 186. An example PDSCH 187 allocation is also shown, herespanning 2 resource blocks (each resource block in LTE comprises afrequency region equal to 12 sub-carriers at 15 kHz spacing, so 180kHz).

In general, the LTE system is constructed with heavy reliance on theprinciple of shared channels. Access to the uplink and downlink sharedchannels within a cell, (UL-SCH and DL-SCH respectively) may be governedby a centralised scheduling function residing within the basestation oreNB. UEs may be notified of uplink or downlink assignments (or “grants”)via control signalling messages carried from the eNB to the UE on aPhysical Downlink Common Control Channel or PDCCH.

Whenever an LTE connected mode UE actively receives a sub-frame (i.e.any non-DRX'd sub-frame), it may search the PDCCH resource region of thesub-frame for any UL or DL assignments directed towards it. The PDCCHresource region may occupy the first NPDCCH OFDM symbols of a sub-framewhere NPDCCH is a variable number (typically from 1 to 4 symbolsdepending on system configuration). If the decoded PDCCH reveals a validassignment for the UE, the UE proceeds to either: for an UL assignment,configure its transmitter in preparation for a forthcoming ULtransmission on the assigned UL resources; or for a DL assignment,decode the corresponding resource portion in the remaining parts of thesame DL sub-frame in which the PDCCH was received.

Note that PDCCH messages may not contain UL or DL assignments and whichare instead used to carry other control-related information such as aninstruction for the UE to carry out a random access procedure. Suchnon-assignment messages are termed “PDCCH orders”.

FIG. 1E is a diagram 188 illustrating construction of an assignmentmessage 189 to a UE. An assignment message 189 of length L1 bits ispassed to a CRC encoder 190 and the resulting CRC 191 is scrambled(bit-wise XOR'd 192) with a UE ID field the same length as the CRC 191(the UE ID may comprise e.g. a Radio Network Temporary Identifier or“RNTI”).

The scrambled CRC 193 is appended to the original message 189 and theconcatenated result is encoded (e.g. by a convolutional or other forwarderror correction encoder 194) to form a total encoded message 195 oflength L2 bits. The length L2 may take one of 4 values, eachcorresponding to a so-called Control Channel Element (CCE) ‘aggregationlevel’ of 1, 2, 4 or 8. By varying the length of the message (L1) priorto encoding and/or the aggregation level (determining L2), the strengthof the forward error correction may be adjusted.

The use of a scrambled CRC 193 provides an efficient means to convey theintended destination user ID to the UE receiver without actuallytransmitting explicit bits for this purpose. Each UE receiver checks theintegrity of the received and decoded CRC only after also performing anequivalent XOR (descrambling) operation with its own user ID. Thus, onlyassignment messages communicated error free over the radio link ANDdecoded by the user with the intended user ID will pass the CRCintegrity check and will be classified as valid assignments. Thepre-encoded assignment message (of length L1 bits) is often referred toas a Downlink Control Information Format (or DCI Format) in the 3GPPspecifications.

The strength of the forward error correction encoding applied to anassignment message may depend upon the pre- and post-encoding messagesizes (L1 and L2). These however are not explicitly indicated by the eNBto the UE and instead the UE may attempt to determine the appliedtransmit encoding via successive trial-and-error decoding attempts usingits knowledge of the different allowable L1 and L2 lengths. Furthermore,in order that multiple assignment messages directed to different UEs maybe flexibly arranged and ‘packed’ into the available PDCCH resourceregion, the UE may search a plurality of possible locations (in additionto the different message lengths) within the PDCCH region for thepresence of any possible assignment for it. This is known as blinddecoding within a defined search space.

The processing loads arising in the UE from blind decoding of PDCCH canbe considerable. The number of possible combinations of message positionand pre/post-encoder message lengths are therefore constrained to alimited number of predefined possibilities; that is, both the number ofFEC encoding possibilities and the search space are reduced. Candidatecombinations of message position and L2 message length are defined. Foreach candidate combination a UE must then check for each of the possibleL1 message lengths by performing a blind decoding operation. In thecurrent LTE system, a UE must typically perform up to 44 blind decodesfor each PDCCH reception instance. This may comprise a search for 2possible L1 message lengths for each of 6 candidate combinations withina so-called “common search space” and a search for 2 further L1 messagelengths for each of 16 candidate combinations within a so-called“dedicated search space” or (interchangeably) “UE-specific searchspace”. (6*2)+(16*2)=44 blind decodes. The same common search space isread by all UEs in the system whereas the locations of the dedicatedsearch spaces may differ for each UE. The dedicated search space for aUE varies on each sub-frame according to a predefined sequence known toboth the UE and the eNB. The predefined sequence is a function of anRNTI associated with the UE.

Each blind decode involves running a tail-biting convolutional codedecoding operation which can contribute to a significant amount ofprocessing and battery drain for a device remaining in connected modefor an extended period, even if in long DRX.

FIGS. 2A and 2B are flowcharts illustrating example methods 200 and 218,respectively, for explicit transitions to a deeper-sleep (e.g. CMDS)sub-state of connected mode. The illustrated method is described withrespect to system 140 of FIG. 1, but this method could be used by anyother suitable system. Moreover, system 140 may use any other suitabletechniques for performing these tasks. Thus, many of the steps in thisflowchart may take place simultaneously and/or in different orders asshown. System 140 may also use methods with additional steps, fewersteps, and/or different steps, so long as the methods remainappropriate.

Generally, in an explicit transition method, the UE 145 may enter theCMDS sub-state in response to at least an explicit message or commandtransmitted by eNB 150. In an eNB-initiated explicit transition method200, the eNB 150 may send or transmit the explicit network message inresponse to an event. In other words, the eNB 150 may detect orotherwise identify an event that triggers the transmission of theexplicit message. A trigger event 220 may be the expiry of a data packetinactivity timer (the timer maintained by the eNB 150), and/or anotherevent.

Alternatively or in combination, in the UE-initiated explicit transitionmethod 218, the UE 150 may first send or transmit a ‘request’ message tothe eNB 150 requesting a transition to the CMDS sub-state based, atleast in part, on knowledge or information determined or otherwiseidentified by the UE 145. In some implementations, this information maybe knowledge or information relating to: the status of applications onthe device (e.g., open, running, closed, dormant), data protocolsassociated with applications on the device (e.g., ‘data transfercomplete’, ‘protocol procedure complete’, ‘data segment acknowledged’),and/or other knowledge or information identified by the UE 145. The‘request’ message may indicate, for example, a high likelihood that nomore packet data is expected for a period of time. Other knowledge orinformation may also be used by the UE 145 when formulating the‘request’ message such as the status of other functions or input to theUE (e.g. screen on/off, presence or absence of user keyboard ortouch-screen input, presence or absence of voice-activated input). Ineither case, the explicit message may be transmitted through one ofseveral protocol layers in the communications system, for example, viaRRC signaling, MAC signaling or L1 signaling.

In either of the two cases shown in FIGS. 2A and 2B, the system 140 mayor may not be configured such that UE 145 returns an acknowledgement(208/230) confirming receipt of the explicit message from the eNB 150.The acknowledgement may be sent at various protocol layers, for example,Radio Resource Control (RRC), RLC, HARQ (L1), and/or others. Anacknowledgement may ensure that both the UE 145 and the eNB 150 have thesame understanding of the UE's current state (CMDS or not). The eNB 150,the UE 145, or both may execute other actions or procedures upon the UE145 entering the CMDS sub-state. For example, requirements for the UE145 to return one or more measurement reporting types that are notconsidered essential for correct operation when in the CMDS sub-statemay be terminated, measurement reporting may be limited to those neededfor mobility-control only, or both. For example, UE reporting related toSelf-Optimising Networks (SON), Automatic Neighbour Relations (ANR) andMinimisation of Drive Test (MDT) purposes may be identified asnonessential measurements, so these measurement configurations may bereleased autonomously in the UE 145 and the eNB 150 on transition to theCMDS sub-state. Alternatively or in combination, their configurationsmay be deactivated by the UE 145 and the eNB 150 upon entering the CMDSsub-state and resumed upon exiting the CMDS sub-state. Requirements forthe UE to transmit one or more uplink control signal types (such as forChannel Quality Indication—CQI, Precoding Matrix Indication—PMI, RankIndication—RI, and uplink Sounding Reference Signals—SRS) may also beterminated upon entering the CMDS sub-state. Such procedures may allowfor improved UE battery savings when in the CMDS sub-state due toreduced UE processing requirements to formulate the measurement reportsor to process UL control signals/feedback and due to the reducedoccurrence of uplink transmission by the UE. Following transmission ofthe explicit message in either method 200 or 218, the UE and eNB may besynchronized in their understanding of when the transition to the CMDSsub-state occurred (e.g., a predetermined period of time following themessage transmission or the acknowledgement transmission).

Referring to FIG. 2A, method 200 begins at step 202 where eNB 150identifies an event trigger associated with transitioning to the CMDSsub-state. At step 204, the eNB 150 determines to transition the UE 145to the CMDS sub-state based, at least in part, on the identified theevent trigger. Next, at step 206, the eNB 150 transmits an explicitmessage to the UE 145 to transition to the CMDS sub-state of the DRXcycle. In response to the explicit message, the UE 208 may transmit anacknowledgement message to the eNB 150. In some implementations, theacknowledgement message may be optional. At step 210, the UE 145transitions to the CMDS sub-state.

Referring to FIG. 2B, the method 218 begins at step 220 where UE 145identifies an event trigger associated with transitioning to the CMDSsub-state. At step 222, the UE 145 transmits a request message to theeNB 150. If the eNB 150 determines not to transition the UE 145 atdecisional step 224, then, at step 226, the eNB 150 waits for furtherevents. If the eNB 150 determines to transition the UE 145, then, atstep 228, the eNB 150 transmits an explicit message to the UE 145 totransitions to the CMDS sub-state. Next, at step 230, the UE 145transmit message acknowledgement to the eNB 145. In someimplementations, the acknowledgement message may be optional. At step232, the UE 145 transitions to the CMDS sub-state.

FIGS. 3A and 3B are flowcharts illustrating example methods 300 and 308for implicit transitions to the CMDS sub-state. In an implicittransition method, the UE 145 may transition to the CMDS sub-state asthe result of an event commonly-known to both the UE 145 and the eNB150. Because the timing of the event is known to both the UE 145 and theeNB 150, the UE 145 may enter the CMDS sub-state without the use of anexplicit signaling message, thereby saving some signaling overhead. Theknown event may include one or more of the following: the expiry of aninactivity timer (such as a time since the last active uplink ordownlink data or packet transmission instance); the expiry of an uplinktiming alignment timer; a DRX cycle counter reaching a pre-determinedthreshold value; a timer expiring or a counter reaching a predeterminedvalue subsequent to the timer or counter having been reset orinitialized based on another DRX sub-state transition (e.g.continuous-Rx to long or short DRX); or others.

Referring to FIG. 3A, method 300 begins at step 302 where the eNB 302identifies an event trigger associated with transitioning to the CMDSsub-state. At step 302, the eNB 150 determines that the UE 145implicitly transitioned to the CMDS sub-state. Referring to FIG. 3B,method 308 begins at step 310 where the UE 145 identifies the eventtrigger associated with transitioning the CMDS sub-state. At step 312,the UE 145 transitions to the CMDS sub-state of the DRX cycle.

In either the explicit transitions discussed in connection with FIGS. 2Aand 2B or the implicit transitions discussed in connection with FIGS. 3Aand 3B, the eNB 145 or UE 150 may be implemented to detect the erroneousevent such that the UE 145 and eNB 150 do not have the sameunderstanding regarding the UEs current status (CMDS or not). Forexample, if the eNB 150 persistently receives no response from the UE145 following PDSCH transmissions, the eNB 150 may infer that the UE 145has moved to the CMDS sub-state and may attempt to contact the UE usingCMDS procedures such as use of a wake-up signal directed to that UE 145.Alternatively or in combination, the UE 145 may need to occasionallycheck for wake-up signals even when the UE 145 identifies a status otherthan the CMDS sub-state, in order to detect the situation wherein theeNB 150 incorrectly believes the UE 145 to be in the CMDS sub-state.

The UE may exit the CMDS sub-state upon certain events. These exitevents may include one or more of the following: receipt of a positivewake-up indicator from the eNB; initiation of resumed UL transmissionprocedures by the UE (e.g., sending of a random access message, ascheduling request message, or other uplink message by the UE); orothers. In response to at least an exit event, the UE 145 may return tonormal (non-CMDS) connected mode operation. If the UE 145 receives apositive wake-up indicator when in the CMDS sub-state, the UE 145 mayexit the CMDS DRX cycle and return to the continuous reception sub-stateof the connected mode.

If the UE 145 determines a need to resume UL transmission when in theCMDS sub-state, the UE 145 may send a preamble on a physical randomaccess channel (PRACH), or the UE may send a scheduling request on aphysical uplink control channel (PUCCH). The choice regarding whether touse the PRACH or the PUCCH to resume UL transmission may depend onwhether the UE is uplink-synchronized to the eNB 150 (determinedaccording to the status of a timing alignment timer) or on whether PUCCHresources for SR have been assigned (by the eNB) to the UE.

On completion of the PRACH procedure or on receipt of an SR on PUCCHresources assigned to the UE 145, the eNB 150 may be able to determinethe identity of the transmitting UE 145, and hence may be able todetermine that the UE 145 has exited the CMDS sub-state. At this point,the eNB 150 and UE 145 may again be synchronized in terms of theirunderstanding of the UE's status (CMDS or not). Optionally, a signal ormessage transmitted by the eNB 150 to the UE 145 may serve as anacknowledgement of its understanding that the UE 145 may no longer be inthe CMDS sub-state. If the UE 145 does not receive such anacknowledgement from the eNB 150 within a certain time period followingits attempts to resume UL transmission from within the CMDS sub-state,the UE 145 may return to the CMDS sub-state and may subsequentlyre-attempt resumption of UL transmission and a successful exit fromCMDS.

When in the CMDS sub-state, the UE 145 may evaluate defined portions oftime that are commonly known to both the UE and the eNB for a wake-upmessage. The eNB 150 may be aware that the UE 145 may not be contactableduring other times. However, for correct system operation, a UE 145 inthe CMDS sub-state may be required to search for certain other signalsor messages. For example, in the current LTE system, connected modeusers may search for paging messages addressed to a Paging Radio NetworkTemporary Identifier (P-RNTI) and which may be sent by the eNB 150during certain pre-defined sub-frames in time. These paging messages mayindicate to all or substantially all connected mode users in the cellthat there has been a change in the cell's broadcast system information.Upon receiving such a paging message on P-RNTI, a connected mode usermay read the updated broadcast system information. The broadcast systeminformation may be sent on the PDSCH using DL assignments sent in thePDCCH region addressed to a System Information Radio Network TemporaryIdentifier (SI-RNTI).

This ability to inform connected mode users of updates to the broadcastsystem information may also be provided to CMDS users. A first solutionmay include the CMDS UEs checking not only for wake-up messages onPDCCH, but also (at the appropriate times) for messages addressed toP-RNTI on PDCCH. The messages addressed to P-RNTI on PDCCH may beassociated with PDSCH transmissions, these containing the systeminformation update indication. A second solution differs from the firstsolution in that it does not include the UE to verify for P-RNTImessages in the PDCCH. Instead, the UE may search for wake-up messageson PDCCH and the eNB 150 sends or transmits one or more wake-up signalsto wake up all or substantially all CMDS users whenever there is achange to system information. This wake-up signal may optionally containinformation enabling the UEs to determine the cause of the wake-up(system information update or otherwise). If the cause of the wake-up iscommunicated the CMDS, UEs 145 may subsequently exit the CMDS sub-stateand read or determine the updated system information. If the cause isnot communicated, the UEs 145 may still exit the CMDS sub-state and as aresult, return to checking the defined sub-frames for messages addressedto P-RNTI. The eNB 150 may then send the paging message which isaddressed to P-RNTI and includes a notification of a system informationupdate. Subsequent to receiving this, the UEs 145 may read or determinethe updated system information messages (which are themselves addressedto SI-RNTI).

FIG. 4 illustrates a sub-frame 400 for transmitting multi-user wake upmessages. In the illustrated implementation, the sub-frame 400 includesa PDCCH resource region 402, and the PDCCH resource region 402 includesthe wake-up message 404. When in the CMDS sub-state, the UE 145 maysearch for the wake-up messages 404 during the PDCCH regions 402 of apre-defined set of sub-frames. The PDCCH wake-up messages 404 may beaddressed to a group of UEs 145 using a group identifier referred to asa wake-up Radio Network Temporary Identifier (w-RNTI). A PDCCH wake-upmessage 402 addressed to a particular w-RNTI may convey wake upindication information for one or more UEs 145 of the group.

A UE 145 may be configured with one or more of the following parametersor information fields that help define the set of possible PDCCH wake-upmessage instances applicable to the UE 145 when in the CMDS sub-state,and to define the formatting of the PDCCH wake-up messages such thatthey may be efficiently and correctly detected and decoded by the UE:parameters defining the DRX pattern behavior; a wake-up RNTI;information regarding the location of the bits associated with the UEsspecific wake-up indicator within the wake-up messages; informationrestricting the pre- and post-encoding sizes of the wake-up messages; orothers. The parameters defining the DRX pattern behavior may include DRXcycle duration, DRX sub-frame offset, DRX Inactivity Timer, or others.These may be the same DRX parameter values as used by the UE 145 whennot in the CMDS sub-state, or may be alternate values that are used bythe UE 145 when in the CMDS sub-state. The alternate (CMDS-specific)values may be individually signaled by the eNB 150 to each UE 145 viadedicated signaling or CMDS-specific values to be used by all CMDS UEs145 may be sent by the eNB 150 via common (broadcast) signaling. Thewake-up RNTI may be explicitly assigned by the eNB 150 to the UE 145using dedicated signaling means. Alternatively or in combination, thewake-up RNTI may be derived by the UE 145 based upon a pre-existing IDfor the same UE 145. The pre-existing UE ID may comprise apreviously-assigned RNTI (e.g., C-RNTI), a subscriber ID (such as aTemporary Mobile Subscriber Identity—TMSI, or an International MobileSubscriber Identity—IMSI), or a device ID (such as an InternationalMobile Equipment Identity—IMEI). The process of deriving may be based ona mathematical formula or a pre-defined associative table mapping thepre-existing UE ID to the UEs CMDS wake-up RNTI. Optionally, theformula, parameters related to the formula, or the associative tableitself may be broadcast to all UEs within the cell by the eNB 150. Thewake-up RNTI may be assigned for a certain duration, for example, theduration of a stay within the CMDS sub-state, or for the duration of astay in connected mode. Information regarding the location of the bitsassociated with the UEs specific wake-up indicator within the wake-upmessages (or other information allowing the UE to decode the commonwake-up message and extract wake-up information specific to that UE).This information may be explicitly assigned by the eNB 150 to the UE 145using dedicated signaling means. Alternatively this information may bederived by the UE 145 based upon a pre-existing ID for the same UE 145.The pre-existing UE ID may comprise a previously-assigned RNTI (e.g.C-RNTI), a subscriber ID (such as a Temporary Mobile SubscriberIdentity—TMSI, or an International Mobile Subscriber Identity—IMSI), ora device ID (such as an International Mobile Equipment Identity—IMEI).The process of deriving may be based on a mathematical formula or apre-defined associative table mapping the pre-existing UE ID to one ormore parameters that collectively provide the UE 145 with theinformation used to decode the common wake-up message and extractwake-up information specific to that UE. Optionally, the formula,parameters related to the formula, or the associative table itself maybe broadcast to all UEs within the cell by the eNB. The information maybe assigned for a certain duration, for example, the duration of a staywithin the CMDS sub-state, or for the duration of a stay in connectedmode. Information restricting the pre- and post-encoding sizes of thewake-up messages (denoted here L1, and L2 respectively) and/orinformation as to where in the PDCCH time/frequency region, the eNB 150may be allowed to transmit a wake-up signal specific to the sharedwake-up RNTI.

The UE 145 may be associated with the above parameters and informationexplicitly, implicitly, or a mixture of the two. In the explicit method,the eNB 150 may assign the parameters or information via explicitsignaling (e.g., RRC signaling, MAC signaling, L1 signaling). In theimplicit method, the UE 145 and eNB 150 may calculate the parameters orinformation based upon a UE ID and a pre-defined formula or associativetable which maps the UE ID to the parameter values or informationfields. The formula or table may be pre-defined or may be described infull or in part via explicit signaling (e.g., broadcast by the eNB 150in the system information of the cell, sent by the eNB 150 via dedicatedsignaling to the UE 145). In a partially-explicit, partially-implicitmethod, the eNB 150 may explicitly assigns one or more of the parametersor information fields to the UE 145 via explicit signaling, whilst thoseparameters that are not explicitly signaled are calculated by the UE 145and eNB 150 based upon a UE ID and a pre-defined formula which maps theUE ID to the remaining parameter values, i.e., a combination of theabove two methods.

Part or all of such CMDS configuration information may bepre-configured, or some/all parameters or information fields may beconfigured at the time of entry into the CMDS sub-state (e.g, carriedwithin the explicit transition message sent by the eNB to the UE), orduring a previous RRC connection establishment, or RRC (re)configurationprocedure.

FIG. 5 is a schematic diagram 500 illustrating details of a downlinktransmission of data to a UE residing initially in the CMDS sub-state.In the illustrated implementation, the diagram 500 includes a pluralityof sub-frames 502 and a graph 504 illustrating UE receiver activationand deactivation. The UE 145 may again operate with a DRX cycle andsub-frame offset (as aforementioned, these may the same or different tothose used when not in the CMDS sub-state). Again, according to theconfigured cycle, the UE 145 may be expected to actively receivesub-frame K (other sub-frames are notionally designated as DRX). Notehowever, that the UE 145 may only be expected to receive the PDCCHregion 506 of sub-frame K (the eNB may not transmit PDSCH data to the UE145 during sub-frame K). In this case, the UE 145 may disable front-endreceiver circuitry of the UE receiver for all non-PDCCH regions of thesub-frame 506, which may allow for processing and battery power savingsin the UE 145 during actively received sub-frames when in the CMDSsub-state compared to normal connected mode operation. Therefore, duringsub-frame K, the UE 145 may receive and buffer only the signal for thePDCCH region 506 or at least a portion of the PDCCH region 506. Afterreceiving the PDCCH region 506, the UE 145 may process the receivedPDCCH signal to identify any included messages addressed to a wake-upRNTI with which the UE 145 is associated and which the UE 145 may sharewith a number of other UEs in the CMDS sub-state.

On sub-frame K, the UE 145 may search for a PDCCH wake-up message 508addressed to a wake-up RNTI associated with the UE 145. This process maybe executed using a blind decoding operation using a convolutionaldecoder to attempt to decode a message of length equal to the knownpre-encoded and post-encoded wake-up message length(s) [aforementionedparameters L1 and L2]. A single length L1 may used in the system forwake-up messages to reduce the blind decoding complexity at the UEreceiver. One or more possible values of L2 may be implemented. Whilstrestriction of L2 to one length may help to further reduce the number ofblind decoding attempts, this restriction may also remove thepossibility to vary the strength of the applied FEC for a fixed L1.Hence to retain some flexibility in the applied FEC strength, more thanone value of L2 may be implemented.

Blind decoding complexity may be reduced (vs. current LTE connected modebehavior) due to the fact that the UE 145 may not check other L1 (andpossibly L2) message lengths in the PDCCH 506 for DL/UL assignments andhence the blind decoding complexity may be reduced. The blind decodingoperation may also check one or more known locations (sets oftime/frequency resources) within the PDCCH region 506 for the presenceof the wake-up message. A reduced number of known locations may be usedto minimize or otherwise reduce the computational complexity associatedwith the blind decoding operation. For example, the UE 145 may includeinformation that the system may transmit wake-up messages on arestricted sub-set of time/frequency regions within the PDCCH 506. Inthis case, the UE 145 may not search for wake-up messages in othertime/frequency locations within the PDCCH 506 outside of the identifiedresources.

An additional possibility is that the particular time/frequencyresources (within the PDCCH 506) on which a wake-up message istransmitted, may be used to identify a sub-set of users to whom themessage is addressed. For example, a sub-set “A” of UEs 145 may beconfigured to search for wake-up messages transmitted on time/frequencyresource set #1, whereas sub-set “B” of UEs 145 may be configured tosearch for wake-up messages transmitted on time/frequency resource set#2. The eNB 150 may send wake-up messages on either (or both) of theresource sets depending on which selected UEs 145 the eNB wishes toaddress. In this case, the same w-RNTI may be used for each set of usersas the message location may identify which set of users is beingaddressed. The search space is not common to all users, nor is itspecific to one user. Instead, the search space may be common to asub-set of users.

In a more generic case where different groups of users search the samecandidate wake-up message locations, multiple wake-up messages may usedifferent w-RNTIs. If a valid PDCCH message 508 associated with the UE'sw-RNTI is detected or otherwise identified, the UE 145 may proceed todetermine the value of its particular wake-up indicator. If theindicator is not transmitted, or its value does not correspond to apositive wake-up indication, the UE 145 may execute no further processesand returns to its DRX duty cycle, remaining in the CMDS sub-state andchecking for further wake-up messages 508 at the next non-DRX'dsub-frame of the configured DRX cycle. If the value of the indicatordoes correspond to a positive wake-up indication, the UE 145 mayactivate the UE receiver to receive signals within the sub-framebeginning “M” sub-frames after the start of sub-frame K (the sub-framein which the PDCCH wake-up message 508 was detected). “M” is thereforethe “wake-up delay” 510 expressed in sub-frame units. By means ofexample, the illustrated value of M is equal to 2, although it will beappreciated that various values of M may be used without departing fromthe scope of the disclosure. During the process, the UE and the eNB maymaintain the same information as to the value of M.

“M” may be the same value for all UEs 145 or may be different valuesper-UE. If a common value for M is used across UEs 145, and this valuemay be a variable parameter, the value may be signaled by the network toall UEs 145 via common signaling. Alternatively or in combination, thevalue of M may be different values for each UE, which may assist inresolving scheduler blocking issues in the time window following asub-frame in which multiple users were woken up. Such UE-specific valuesof M may be explicitly signaled or assigned to the UE 145 by the eNB 150(such as via RRC signaling, or even within the wake-up messageitself—this may include multiple bits per wake-up indicator to signalthe value of M to the UE 145), or may be implicitly derived based upon auser ID such as an RNTI, IMSI or TMSI. Different protocol layers (e.g.RRC, MAC, L1) may be used to signal M.

As an extension to this principle, the UE 145 may also be configuredwith a further parameter Z, and may configure the UE receiver toactively receive a defined “window” of sub-frames of length Z followingreceipt of a positive wake-up indication. For example, the window maycomprise the Z sub-frames from (K+M) to (K+M+Z−1). In doing so, the eNB150 may distribute the pending PDSCH transmissions to multiplesimultaneously-woken UEs within the time window of Z sub-frames, ratherthan being restricted to addressing all UEs PDSCH assignments within atime window of just one sub-frame. Hence, scheduler blocking issues maybe alleviated. In the illustrated implementation, Z=1.

Following transmission of the wake-up message 508 in sub-frame K, theeNB 150 may then determine that the UE 145 will receive the (K+M)thsub-frame and then transmit a PDSCH assignment message 512 during thePDCCH region 514 and to transmit the DL data during the PDSCH region 516of the sub-frame. The PDSCH assignment 512 may be transmitted in thePDCCH region 514 of sub-frame K+M and uses a UE-specific RNTI (such asC-RNTI) as per normal connected mode operation in LTE. The inactivitytimer 518 may be restarted in sub-frame K+M due to the presence of theDL assignment and the timer may continue to run in this example for 2further sub-frames (the length of the DRX inactivity timer 518). In thisexample, no further data may be communicated during those sub-frames andthe UE 145 may hence return either to a long or short DRX sub-state(subsequently to the CMDS sub-state if inactivity continues) or directlyto the CMDS sub-state (if the system is configured to allow this directtransition).

FIGS. 6A-C are schematic diagrams 600, 620, and 640 illustratingsequences when no data is transmitted. In particular, diagram 600illustrates when sub-frame K does not contain a PDCCH wake-up messageaddressed to the UEs w-RNTI. In this event, the UE 145 may not receivesub-frame K+M, and the UE 145 may return to the DRX cycle and receivesthe PDCCH region of sub-frame K+LDRX to check once again for thepresence of a valid wake-up indicator. Diagram 620 illustrates a processwhen sub-frame K does contain a PDCCH wake-up message addressed to theUEs w-RNTI, but the UE determines that the message indicates it shouldnot wake-up. In this event, the UE 145 also may not receive sub-frameK+M. The UE 145 may return to its DRX cycle and receive the PDCCH regionof sub-frame K+LDRX to check once again for the presence of a validwake-up indicator. Diagram 640 illustrates a process when sub-frame Kdoes contains a PDCCH wake-up message addressed to the UEs w-RNTI andthe UE interprets that the message indicates that it should wake-up.This may be a result of the eNB 150 attempting to wake-up another UE 145b and the particular formatting of the wake-up message may not haveallowed for this to occur without also waking up this UE 145 a (e.g.,multiple UEs share the same indicator). In this (false-alarm) event, theUE 145 may receive sub-frame K+M but may not identify a PDSCH assignmentmessage addressed to it within the PDCCH region of that sub-frame. TheUE returns to its normal DRX cycle of operation and will receive thePDCCH region of sub-frame K+LDRX to again check for the presence of avalid wake-up indicator. As has been previously described, the PDCCHprocessing complexity during the actively-received sub-frames may alsobe reduced when compared to the case of current LTE connected modeoperation by virtue of the fact that the number of blind decodes mayreduced. The resulting reduction in UE battery drain may provide forextended times between battery recharges, or may enable the network toset shorter DRX cycle times whilst preserving the same time between UEbattery recharges. These shorter DRX cycle times may in-turn offerreduced latency, and improved user experience and system performance.

A wake-up message in the PDCCH region may comprise L_(W) informationbits in addition to L_(CRC) bits for the CRC/RNTI such thatL₁=L_(W)+L_(CRC). In general, the CRC appended to a DCI format messagemay comprise a Cyclic Redundancy Check computed over the length L_(W) ofthe DCI format and this may subsequently be bitwise exclusive-OR'd(XOR'd) with a 16-bit RNTI value such as a w-RNTI, a C-RNTI, a P-RNTI,an RA-RNTI, an SPS-RNTI or an SI-RNTI. The PDCCH wake-up messagelength(s) may be arranged to be equal to the lengths of pre-existing DCIformats in the LTE system. In this way, the message lengths may becompatible with the existing LTE physical layer thereby minimising orotherwise reducing the need for redesign when accommodating the proposedwake-up message functionality on PDCCH.

Table 1 lists example sizes (in bits) of the existing DCI formats 1C and3/3A. L₁ is the length in bits of the DCI format with a 16-bit CRC andL_(W) is the length in bits of the DCI format without the 16-bit CRC.The value N_(RB) denotes the number of 180 kHz resource blocks definedwithin the system bandwidth. The use of PDCCH wake-up message lengthsother than those shown in Table 1 is not precluded.

TABLE 1 Sizes (in bits) of existing DCI formats 1C and 3/3A DCI format1C DCI format 3/3A System Without With Without With BW N_(RB) CRC(L_(W)) CRC (L₁) CRC (L_(W)) CRC (L₁) 1.6 MHz  6 8 24 20 36  3 MHz 15 1026 22 38  5 MHz 25 12 28 24 40 10 MHz 50 13 29 26 42 15 MHz 75 14 30 2743 20 MHz 100 15 31 28 44

A PDCCH wake-up message instance is defined as a PDCCH transmission on aparticular sub-frame and using a particular w-RNTI. The L_(W)information bits within a PDCCH wake-up message allow for one of up toN_(cw)=2^(Lw)−1 possible wake-up codewords to be transmitted for thatinstance.

A number (N_(UE)) of UEs may be configured to listen to the PDCCHwake-up message instance and to each decode the transmitted wake-upcodeword. Each UE may decode the codeword in order to extract wake-upinformation of relevance to that UE (for example, to determine whetheror not it should wake-up).

FIG. 7 is a codeword system 700 that shows a set of wake-up indicators702 a-m (one for each of the N_(UE) UEs) being encoded by the eNB 150 inorder to produce a wake-up codeword of length L_(W) bits 703. Thecodeword may be subject to appropriate forward error correction encodingprior to transmission. This correction may comprise CRC attachment andconvolutional encoding in which: for each codeword (i.e. wake-upmessage) a CRC may be calculated over the L_(w) bits it contains; theCRC may be appended to the data after being scrambled using a specificwake-up RNTI (w-RNTI); and convolutional encoding may be performed onthe concatenated sequence comprising the codeword and CRC bits.

The transmitted PDCCH wake-up message instance is subsequently receivedby a plurality of UEs. Following appropriate forward error correctiondecoding of the PDCCH, each UE is then in possession of the same L_(w)decoded PDCCH bits comprising the received wake-up codeword. Each UEdecodes the codeword in order to determine the value of the wake-upindicator 704 a-m of relevance to that particular UE. Thus, the step ofcodeword decoding may be specific to each UE.

In general, the wake-up indicators for each UE may be binary ormulti-valued. For example, a binary indicator may be used to simplyindicate “wake-up” or “do no wake-up”. Multi-valued indicators may allowfor the carriage of additional information to the UE, and to providefurther functionality or flexibility. For example, a multi-valuedindicator may be used to indicate “wake-up in M sub-frames time” wherethe value of M is signalled within the indicator value.

A large variety of possibilities exist regarding how the indicators aremapped to wake-up codewords on the PDCCH. The mappings may be designedto optimise particular performance attributes of the communicationscheme. Such performance attributes may include: wake-up messagingcapacity (e.g., attempt to maximise the number of UEs that may beaddressed via a single PDCCH wake-up codeword); false alarm probability(e.g., attempt to minimise the probability that a UE incorrectlyinterprets a transmitted wake-up codeword to mean it should wake-up,when such action was not intended by the eNB); wake-up messagecommunication reliability (e.g., using a repetition or block code toproduce multiple bits per indicator prior to the existing FEC encodingoperation—this may be used to further increase the level of FECprotection).

FIGS. 8A-D illustrates example mappings 800, 820, 840, and 860 betweencodewords and positions or values of wake-up indicators. In theseexamples, the PDCCH wake-up message length is selected to be L_(W)=13bits, equal to the length of DCI format 1C for an LTE system with 10 MHzsystem bandwidth. FIG. 8A shows a first (and simple) example codewordmapping 800 in which each indicator is binary valued and is mappedexclusively to a single bit position (1 . . . L_(W)) within the wake-upcodeword. This results in N_(UE)=13 UEs that may be associated with thesame PDCCH wake-up message instance. In this implementation, multiplePDCCH message instances may exist within the same sub-frame, these beingdistinguished by means of their differing w-RNTIs. A total of 2 w-RNTIsare shown, and therefore a total of 2×N_(UE)=26 users may receivewake-up indicators within the same sub-frame.

FIG. 8B shows a second example codeword mapping 620 in which each of theUE indicators is again binary valued. In this example however, bit “i”within the codeword is set based upon a logical OR of N_(share)=4 UEindicators. More specifically, in this example bit “i” is set based onan OR of the indicators for UEs: {i, i+L_(W), i+2L_(W), i+3L_(W)}. Thus,if any one of the UEs need to be woken-up, all 4 UEs associated with thesame indicator will actually be woken-up regardless of whether they tooshould have been woken (i.e. this scheme carries a risk of false-alarmwake-up). The figure again shows that multiple PDCCH wake-up messageinstances may exist within the same sub-frame, these being distinguishedby means of their differing w-RNTIs. A total of 2 w-RNTIs are shown, andtherefore a total of 2×N_(share)×N_(UE)=104 users may receive wake-upindicators within the same sub-frame. The scheme is extensible to othervalues of N_(share).

FIG. 8C shows a third example codeword mapping, in which each of the UEindicators is again binary valued. The mapping of the UE indicators tothe wake-up codeword is more complex in this example. In a first step,the indicator for the n^(th) UE (each of N_(UE) UEs) is first associatedwith an intermediate codeword C_(n). C_(n) is of length L_(W) bits. Ifthe UE indicator is set FALSE (i.e. “do not wake-up”), C_(n) is a vectorof L_(W) zero's. If the indicator is set TRUE, C_(n) is set to aUE-specific vector V_(n) of L_(W) bits, constrained such that only N₀ ofthe bits in V_(n) are set TRUE. Second, the final codeword C_(final) oflength L_(W) bits is constructed via a logical bitwise OR operationacross all of the N_(UE) intermediate codewords (C_(n)) formed in thefirst step. Thus, with “i” indicating the bit position,C_(final)(i)=(C₁(i)|C₂(i)|C₃(i) . . . |C_(Lw)(i)). The above representsone implementation of this scheme. It shall be appreciated that thisimplementation is not limiting and that the same result may be achievedvia other implementations. For example, the scheme may be alternativelyexpressed as: each UE for which the UE indicator is to be set TRUE isassociated with N₀ bit positions within the codeword of length L_(W)bits; and bits within the final codeword C_(final) of length L_(W) bitsare set TRUE if they correspond to any of the bit positions associatedwith the UEs for which the UE indicator is TRUE. In the example of FIG.8C, N₀=2 for all UEs. Different values of N₀ for different UEs are alsopossible. For example the N₀ for a particular UE could vary depending onthe likelihood of a positive wake-up indication being sent to that UE;i.e. a UE that receives data infrequently (and is thus less likely toreceive a positive wake-up indication) could use a larger value of N₀than a UE that receives data more frequently (and is thus more likely toreceive a positive wake-up indication). When decoding the receivedcodeword, each UE checks to see whether ALL of the non-zero bitpositions associated with its V_(n) are set to TRUE. Only if all ofthese bit positions are set to TRUE will the UE wake-up. For example, tocarry out this operation, the UE may mask the L_(W) received bits withthe known V_(n) codeword that is specific to this UE. The maskingoperation is typically a bitwise AND operation of the received codeword(C_(final)) with V_(n). If the sum of the number of bits that are setTRUE in the resulting masked codeword is equal to N₀, the UE interpretsthis as a positive wake-up indication, otherwise the UE interprets thereceived codeword as a negative wake-up indication. In this thirdexample, in order to minimise or otherwise reduce the false alarmprobability, the positions of any non-zero bits in V_(n) for this UEpreferably overlap as little as possible with the positions of anypotential non-zero bits in V_(n) for other UEs. If there is no overlap,there is zero false alarm probability. However, the probability of falsealarm may be a function of: the proportion of wake-up indicators set toTRUE this wake-up instance (within the set of N_(UE)); the value ofN_(UE); the value of N₀; and the length L_(W). That is, variations inthe above affect the probability that certain combinations of UEs with apositive wake-up indication correspond (unintentionally) to a positivedecoded wake-up indication for another UE. The eNB may individuallysignal the V_(n) codeword itself (or equivalently the positions of thenon-zero bits within V_(n)) to each of the relevant UEs. Alternatively,V_(n) may be derived (by the eNB and by the UE) by means of a hashingfunction or other computational or algorithmic means. The hashingfunction or other computational or algorithmic means may require inputof the value L_(W) and of a UE ID (such as a pre-existing C-RNTI, a TMSIor an IMSI), and may output V_(n) codeword values of length L_(W), orequivalently, the bit positions within V_(n).

FIG. 8C shows two w-RNTI in use, with N_(UE)=30 for the first w-RNTI andN_(UE)=20 for the second w-RNTI (thus wake-up indicators may be sent toup to 50 UEs within the same sub-frame). In the particular exampleshown, V_(n) for the UEs shown would equal:

UE 1, V_(n)=[1001000000000]

UE 2, V_(n)=[0100010000000]

UE 3, V_(n)=[0001000100000]

UE 30, V_(n)=[0000000100001]

UE 31, V_(n)=[1000010000000]

UE 32, V_(n)=[0101000000000]

UE 33, V_(n)=[0010010000000]

UE 50, V_(n)=[0000000010100]

N_(UE) may take a range of values depending upon the desired false alarmprobability and the desired wake-up message capacity. It will beappreciated that use of only a single w-RNTIs is also possible.

FIG. 8D shows a fourth example codeword mapping, in which each of the UEindicators is again binary valued. The mapping of the UE indicators tothe wake-up codeword follows the steps outlined for the third example ofFIG. 8C. However, in this case, the value of N₀ used for a given PDCCHwake-up message is signalled by means of the w-RNTI used to transmit themessage. The mapping 860 illustrates two sub-frame instances with asingle PDCCH wake-up message per sub-frame. This scheme differs fromthat of FIG. 8C in that the w-RNTI used for PDCCH wake-up messagetransmission is not used to distinguish multiple PDCCH messages withinthe same sub-frame, but is instead used to signal to the UEs, the valueof N₀ that is in use for this sub-frame. This allows the eNB to adjustthe false alarm probability depending on the number of UEs that have apositive page indication within a PDCCH wake-up message.

In the illustrated implementation, w-RNTI #1 in the first sub-frameinstance is used to indicate that a value of N₀=2 is in use, whilst inthe second sub-frame instance, the (different) w-RNTI #2 is used toindicate that a value of N₀=3 is in use. The UEs receiving the PDCCHwake-up message first determine the w-RNTI value that has been used, anduse this to look-up a corresponding value of N₀. The UEs then configuretheir codeword decoders (and determine or select V_(n)) in accordancewith the determined value of N₀. N_(UE)=20 is shown for each of the twoPDCCH wake-up message instances.

This ability to dynamically vary N₀ on a per sub-frame basis may be usedby the eNB in order to optimise the false alarm probability based uponits knowledge of how many UEs will have a positive wake-up indicator setwithin this PDCCH wake-up message. The eNB is able to count the numberof UEs that will be falsely woken-up for different values of N₀ and mayselect the value of N₀ that results in the lowest number of falselywoken-up UEs.

As an optional feature, the eNB may decide not to transmit the wake-upmessage at all (i.e. DTX), in the event that no positive wake-upindicators are transmitted for any of the UEs associated with a PDCCHwake-up message instance. By doing so, the eNB may be able to save powerand transmission resources and to use these for other(non-wake-up-related) transmissions.

FIG. 9 is a schematic diagram 900 illustrating time domain multiplexingof wake-up messages within a DRX cycle length (of L_(DRX) sub-frames).As previously mentioned, a PDCCH wake-up instance may be defined interms of a sub-frame instance and a particular w-RNTI. Given that UEslistening for the wake-up indicators would typically be assigned a DRXcycle (and a DRX sub-frame offset for that DRX cycle, defining whichsub-frames the UE actively listens for wake-up messages), time-domainmultiplexing of PDCCH wake-up instances (and hence of UE indicators) isalso possible. This may be used to increase the number of availablewake-up indicators in the system. For example, each CMDS UE in thesystem may be associated with at least a triplet of parameterscomprising {DRX sub-frame offset, w-RNTI, and UE indicator positionwithin the PDCCH wake-up message}.

In this example, a total of “Q” w-RNTIs are reserved in the system forwake-up messages. The DRX cycle length is configured to be L_(DRX)sub-frames in duration, and each wake-up message comprises N_(UE)wake-up indicators (these being mapped to wake-up codewords of lengthL_(W) bits as previously described in FIG. 7). In such a configuration,the maximum number of supportable CMDS users is equal to:

For example, assuming a DRX cycle length L_(DRX)=320, Q=2, andN_(UE)=13, the number of users that may be supported (per cell) in theCDMS sub-state is 8320.

In general, not all sub-frames of the DRX cycle may be used forpotential wake-up messages. It is also possible to employ wake-upmessages with increased payload sizes (e.g. larger L_(W) or largerN_(UE)) but which are available on only a sub-set of the sub-frameswithin the DRX cycle. For example, the same number of 8320 CMDS usersper cell could be supported using DCI format 3/3A (L_(W)=26 bits for 10MHz system bandwidth) and with N_(UE)=26, but with wake-up messagespossible on only half of the sub-frames within the same 320 sub-frameDRX cycle. Assuming a fixed probability (per-sub-frame duration) thatdata arrives for a UE (therefore needing to be woken up at the nextavailable opportunity), this has the effect of increasing the averagenumber of UE indicators that need to be set to TRUE per PDCCH wake-upmessage instance and hence the total number of wake-up messages thatneed to be transmitted may be reduced without extending the DRX cyclelength for each user. In general, the system may be optimised byadjusting one or more of: the UE indicator capacity of the PDCCH wake-upmessage (N_(UE)) [this may be further dependent on L_(W), N₀,N_(share)]; the number of w-RNTIs; the DRX cycle length (L_(DRX)); andthe allocation of DRX sub-frame offsets to users (and hence the fractionof all sub-frames that may be used for wake-up message opportunities).

FIG. 10 is a schematic diagram 1000 that illustrates a single-user(dedicated) wake-up message addressed to a UE-specific RNTI (e.g. aC-RNTI) and transmitted during the PDCCH region of a sub-frame. In thissolution, a PDCCH message (DCI format comprising L_(W) information bits)contains a dedicated wake-up signal specific for only one UE (this UEresiding in the CMDS sub-state). The wake-up signal may take the form ofa normal UL or DL assignment addressed to the UEs dedicated RNTI (i.e.C-RNTI). The eNB may transmit the dedicated wake-up message during thePDCCH region of any actively-received (non-DRX) sub-frame (as per thecurrent LTE design). The distinction in this solution from the currentLTE design however, is that the PDSCH associated with the DL assignmentis delayed into another sub-frame (i.e. a time-gap still exists betweenthe PDCCH wake-up and the PDSCH as per the previously-describedmulti-user wake-up solutions). As a result, a UE still need onlyactivate its front-end receiver circuitry for the PDCCH region of eachnon-DRX sub-frame when in the CMDS sub-state (and may DRX the PDSCHregion). Thus, in this solution, DL communications between an eNB and aUE may take one of two forms: (1) when in the CMDS sub-state, a DLassignment in the PDCCH region of sub-frame K is associated with a PDSCHtransmission in sub-frame K+M (where the value of M is configured,dynamically signalled or pre-defined); and (2) when not in the CMDSsub-state, a DL assignment in the PDCCH region of sub-frame K isassociated with a PDSCH transmission in the same sub-frame K (normal LTEoperation).

Systems are known in the prior art in which a time-gap (or time-slot orsub-frame gap) exists between a DL assignment and the transmission ofthe associated DL data. For example, the FDD UMTS HSDPA system comprisesa control channel termed the HS-SCCH and a DL data channel termed theHS-PDSCH. Both the HS-SCCH and the HS-PDSCH are 2 ms (3 timeslots) induration, yet the HS-PDSCH starts 2 timeslots after the start of theHS-SCCH. However, these known systems utilise a fixed time gap betweenthe control channel and the associated data channel.

In the proposed solution of FIG. 10, the sub-frame time gap between thecontrol (PDCCH) and the PDSCH (data) is variable between at least twovalues: (1) no time gap when not in a deeper sleep state (active UEs);and (2) a time gap of length M sub-frames when in a deeper sleepsub-state (inactive UEs). Thus, the low data transfer latency achievablewith no time gap remains available for active UEs, whilst improved UEpower/battery consumption is enabled for inactive UEs (at the expense ofa small latency penalty for the first transmission upon exiting thesleep state).

FIGS. 11A and 11B are schematic diagrams 1100 and 1130 illustratingwake-up using normal DL assignment on PDCCH but with delayed PDSCH. Thediagram 1145 illustrates a CMDS UE searching for such a wake-up messageon C-RNTI during non-DRX sub-frame K. The wake-up signal is effectivelya normal DL (or potentially UL) assignment on PDCCH, and is sent usingthe UE-specific C-RNTI. However, the associated PDSCH transmission isdelayed by M sub-frames (note that M could be any of a fixed value, aconfigurable value common amongst UEs, or a UE-specific value in thesame ways as previously described for the multi-user wake-up solutions).Because the wake-up signal sent on the PDCCH of sub-frame K iseffectively the same as a normal DL assignment message, it thereforecontains the parameters that are needed to describe the physicalresources and formatting of the forthcoming PDSCH transmission (but hereon sub-frame K+M rather than on sub-frame K). Thus, in sub-frame K, avalid DL assignment message is detected by the UE and this is used as atrigger to wake up from the CMDS sub-state and to return to normaloperation and the associated PDSCH transmission is delayed untilsub-frame K+M.

When in the UE is in the CMDS sub-state (as it is in this example duringsub-frame K), the UE may interpret reception of the C-RNTI assignmentmessage on the PDCCH in sub-frame K as a “delayed” assignment and maysubsequently execute data reception procedures as if a normal C-RNTIassignment message had been received in sub-frame K+M. That is, fromsub-frame K+M onwards, the UE may “act” in the same way as a non-CMDS UEwould have if it had received a normal C-RNTI assignment.

Depending on the system design, the DRX inactivity timer may berestarted either at sub-frame K (due to the presence of the initialC-RNTI assignment message on the PDCCH), or at sub-frame K+M (due to thepresence of the PDSCH or because the UE is acting “as if” it hadreceived an assignment message on sub-frame K+M). It is the latter casethat is shown in FIG. 11A in which the timer then continues to run for afurther 2 sub-frames (the length of the DRX inactivity timer).

The UE therefore receives the PDSCH in sub-frame K+M and restarts theDRX inactivity timer as would be the case for any normally-receivedPDSCH transmission. In this example, the DRX inactivity timer durationis set to 2 sub-frames (meaning that two further sub-frames beyondsub-frame K+M are received if no further data activity takes place).Note that the PDCCH in sub-frame K+M need not necessarily contain a DLassignment for the UE as this has already been received in sub-frame K.Preferably however, the eNB should not make a DL assignment (using thesame PDCCH resources) to another UE in sub-frame K+M in order to avoidthe potential for collision of ACK/NACK transmissions from two UEs onPUCCH uplink resources that are linked to the PDCCH resources used forthe DL assignments. This does not preclude the eNB from sending othercontrol messages (not DL assignments) to the UE (or another UE) duringthe PDCCH region of sub-frame K+M, or from sending a DL assignment that‘overwrites’ that received in sub-frame K.

After sub-frame K+M, subsequent DL transmissions to the UE on anarbitrary sub-frame (Y) whilst not in the CMDS sub-state would be madeusing a DL assignment during the PDCCH region of sub-frame Y and anassociated PDSCH transmission within the same sub-frame. Thus, there isno further sub-frame time-gap between the PDCCH and the PDSCH so long asthe UE is not in the CMDS sub-state.

In FIG. 11B, the diagram 1170 illustrates a situation in which a CMDS UElistens for a wake-up message using C-RNTI on sub-frame K, but a validDL (or UL) assignment message is not detected (hence the UE determinesit should remain in the CMDS sub-state). The UE sleeps until the nextDRX cycle (sub-frame K+L_(DRX)) where it once again checks for thepresence of a wake-up signal/DL or UL assignment using C-RNTI.

FIG. 12 shows an example of radio station architecture for use in awireless communication system. Various examples of radio stationsinclude base stations and wireless devices. A radio station 1205 such asa base station or a wireless device can include processor electronics1210 such as a processor that implements one or more of the techniquespresented in this document. A radio station 1605 can include transceiverelectronics 1215 to send and receive wireless signals over one or morecommunication interfaces such as one or more antennas 1220. A radiostation 1605 can include other communication interfaces for transmittingand receiving data. In some implementations, a radio station 1605 caninclude one or more wired network interfaces to communicate with a wirednetwork. In other implementations, a radio station 1605 can include oneor more data interfaces 1230 for input/output (I/O) of user data (e.g.,text input from a keyboard, graphical output to a display, touchscreeninput, vibrator, accelerometer, test port, or debug port). A radiostation 1605 can include one or more memories 1240 configured to storeinformation such as data and/or instructions. In still otherimplementations, processor electronics 1210 can include at least aportion of transceiver electronics 1215.

1. A method in a user equipment (UE) comprising: activating the UEreceiver during a control portion of a sub-frame including controlinformation; and after receiving the control portion, deactivating theUE receiver during a data-traffic portion of the sub-frame.
 2. Themethod of claim 1, further comprising: decoding the control portion toidentify a wake-up message for the UE, the wake-up message configured toactivate the UE receiver in a subsequent sub-frame; and activating theUE receiver during both a control portion and a data-traffic portion ofthe subsequent sub-frame.
 3. The method of claim 2, wherein the wake-upmessage identifies at least one of a total number of sub-frames to delayprior to activating the UE receiver during the data-traffic portion or atotal number of sub-frames, including the subsequent sub-frame, toactivate the UE receiver during the data-traffic portion.
 4. The methodof claim 1, wherein the UE receiver is activated for three or fewersymbols of the control portion and is deactivated on subsequent symbolsof the sub-frame.
 5. The method of claim 1, further comprisingreceiving, from a Base Station (BS), an explicit message to transitionthe UE to a Connected Mode Deep Sleep (CMDS) state, the CMDS stateconfigured to deactivate the UE receiver during data-traffic portions ofsub-frames.
 6. The method of claim 1, further comprising transmitting arequest to the BS to transition to the CMDS state in response to the UEidentifying a trigger event.
 7. The method of claim 1, wherein the UEreceives the explicit message independent of initially transmitting arequest to the BS.
 8. The method of claim 1, further comprisingtransmitting, to the BS, an acknowledgement indicating a transition tothe CMDS sub-state.
 9. The method of claim 1, further comprising:determining a wake-up message included in the control portion identifiesa wake-up IDentifier (ID) assigned to a group of UEs including the UE;and determining a wake-up indicator for the UE included in the wake-upmessage in response to determining the wake-up RNTI, the wake-indicatorconfigured to indicate whether to activate the UE receiver duringdata-traffic portions of a sub-frame.
 10. The method of claim 9, furthercomprising determining a number of wake-up indicators for the UEincluded in the wake-up message, the number of wake-up indicators beingdetermined based upon the wake-up RNTI used to transmit the wake-upmessage.
 11. The method of claim 9, wherein determining the wake-upindicator comprises: decoding the wake-up message to identify a codewordassociated with the wake-up ID; and decoding the codeword using analgorithm assigned to the UE, each of the UEs assigned a differentalgorithm.
 12. User Equipment (UE), comprising: one or more processorsconfigured to: activate a UE receiver during a control portion of asub-frame including control information; and after receiving the controlinformation, deactivating the UE receiver during a data-traffic portionof the sub-frame.
 13. The UE of claim 12, the processors furtheroperable to: decode the control portion to identify a wake-up messagefor the UE, the wake-up message configured to activate the UE receiverin a subsequent sub-frame; and activate the UE receiver during both acontrol portion and a data-traffic portion of the subsequent sub-frame.14. The UE of claim 13, wherein the wake-up message identifies at leastone of a total number of sub-frames to delay prior to activating the UEreceiver during the data-traffic portion or a total number ofsub-frames, including the subsequent sub-frame, to activate the UEreceiver during the data-traffic portion.
 15. The UE of claim 12,wherein the UE receiver is activated for three or fewer symbols of thecontrol portion and is deactivated on subsequent symbols of thesub-frame.
 16. The UE of claim 12, the processors further operable toreceive, from a Base Station (BS), an explicit message to transition theUE to a Connected Mode Deep Sleep (CMDS) state, the CMDS stateconfigured to deactivate the UE receiver during data-traffic portions ofsub-frames.
 17. The UE of claim 12, the processors further operable totransmit a request to the BS to transition to the CMDS state in responseto the UE identifying a trigger event.
 18. The UE of claim 12, whereinthe UE receives the explicit message independent of initiallytransmitting a request to the BS.
 19. The UE of claim 12, the processorsfurther operable to transmit, to the BS, an acknowledgement indicating atransition to the CMDS sub-state.
 20. The UE of claim 12, the processorsfurther operable to: determine a wake-up message included in the controlportion identifies a wake-up IDentifier (ID) assigned to a group of UEsincluding the UE; and determine a wake-up indicator for the UE includedin the wake-up message in response to determining the wake-up RNTI, thewake-indicator configured to indicate whether to activate the UEreceiver during data-traffic portions of a sub-frame.
 21. The UE ofclaim 20, the processors further operable to determine a number ofwake-up indicators for the UE included in the wake-up message, thenumber of wake-up indicators being determined based upon the wake-upRNTI used to transmit the wake-up message.
 22. The UE of claim 20,wherein the processors operable to determining the wake-up indicatorcomprises the processors operable to: decode the wake-up message toidentify a codeword associated with the wake-up ID; and decode thecodeword using an algorithm assigned to the UE, each of the UEs assigneda different algorithm.